This invention relates to apparatus for pulverizing, i.e., grinding, material, and more specifically to a journal bearing system that is particularly suited for embodiment in a bowl mill wherein the journal bearing system is operative for purposes of providing the bearing support for the journal shaft on which the pulverizer, i.e., grinding, roll is suitably mounted.
It has long been known in the prior art to provide apparatus that is suitable for employment for purposes of effecting the grinding, i.e., pulverization, of materials. More specifically, the prior art is replete with examples of various types of apparatus that have been used heretofore to effect the grinding of a multiplicity of different kinds of materials. In this regard, in many instances discernible differences of a structural nature can be found to exist between individual ones of the aforesaid apparatus. The existence of such differences is in turn attributable for the most part to the diverse functional requirements that are associated with the individual applications in which such apparatus are designed to be employed. For instance, in the selection of the particular type of apparatus that is to be utilized for a specific application one of the principal factors to which consideration must be given is that of the nature of the material that is to be ground in the apparatus. Coal is one such material wherein there exists a need to grind the material in order to render it suitable for use in certain applications. Furthermore, fossil fuel fired power generation systems represent one such application in which it is desired to employ coal, as the source of fuel therefor, and wherein a requirement exists to grind, i.e., pulverize the coal in order to render it suitable for use for this purpose.
To this end, coal has long been recognized as being one of this nation's most abundant sources of fuel. At one time earlier in this century, much of the nation's energy needs were being met through the use of coal. Then, in the degree to which coal was being employed to generate power a decline set in. Much of this decline stemmed from the increased usage of oil and gas as sources of fuel. More recently, the power being generated from the burning of oil and gas has been supplemented by the use of nuclear fuel for power producing purposes. However, with the advent of the oil embargo in the last decade which was accompanied by sharp increases in the price of oil and the existence of restricted oil supplies, and the increased concern, which has since been expressed over the rate at which the world's known oil reserves are being depleted, coal has begun to regain some of the favor, which it once had as a source of fuel to meet the nation's energy needs. To some extent, this has been evidenced in the number of orders, which have been placed in recently past years, for power generation systems that are to be coal fired as well as the extent to which increased interest has been shown in effecting the conversion of existing oil and gas fired power generation systems to coal fired systems.
For purposes of the discussion that follows, the coal fired systems referred to above are considered to consist of essentially the following major operating components: a coal feeder, apparatus for pulverizing the coal, a distribution system for distributing the coal after the pulverization thereof, a furnace in which the coal is to be burned, and the requisite controls for effecting the proper operation of the coal fired power generation system. Of particular interest herein is that portion of the coal fired system, which has been identified above as the apparatus for pulverizing the coal. Coal pulverizing apparatus are not new. They have been known to exist in the prior art for more than half a century. Furthermore, many improvements in the construction and/or mode of operation of coal pulverizing apparatus have been made during this period.
There are a number of features that it is advantageous for any coal pulverizing apparatus to possess, but particularly those which are designed for employment in a coal fired power generation system. Reference is had here to features such as reliability, low power consumption, minimum maintenance and wide range of capacity. In addition, such apparatus advantageously should also be characterized by quiet operation, integrated lubrication systems, convenient adjustment and control of coal flow and fineness, and the ability to handle the high temperature air that is required for high moisture coal.
One particular type of coal pulverizing apparatus, which is to be found in the prior art, that is advantageously characterized by the embodiment therein of the above recited features is an apparatus, most commonly referred to in the industry by the name bowl mill. The latter apparatus obtains its name by virtue of the fact that the pulverization, i.e., grinding, of the coal which takes place therein is effected on a grinding surface that in configuration bears a resemblance to a bowl.
Reference may be had by way of exemplification to U.S. Pat. No. 3,465,971, which issued Sept. 9, 1969 to J. F. Dalenberg, et al., and/or U.S. Pat. No. 4,002,299, which issued Jan. 11, 1977 to C. J. Skalka, both of the latter patents being assigned to the same assignee as the instant application, for a teaching of the nature of the construction and the mode of operation of a prior art form of bowl mill that is suitable for use in a coal fired power generation system to effectuate the pulverization of the coal that is to be burned as fuel therein. As taught by the aforereferenced patents, a bowl mill essentially consists of a body portion in which a grinding table is mounted for rotation, a plurality of grinding rollers that coact with the grinding table to effect the grinding of coal interposed therebetween, coal supply means for feeding to the interior of the bowl mill the coal that is to be pulverized and air supply means for supplying to the interior of the bowl mill the air required in the operation of the latter. In accordance with the mode of operation of such a bowl mill, the coal, which enters the bowl mill, is pulverized by virtue of the coaction of the grinding rollers with the grinding table. After being pulverized, the coal particles are thrown outwardly by centrifugal force whereby the particles are fed into a stream of air that is entering the bowl mill. The stream of air, which now contains pulverized coal particles, flows through a tortuous path that is established in part by the positioning within the bowl mill of a suitably supported deflector means. As the stream of air and coal particles flows along the aforementioned tortuous path, the sharp turns contained therein effects the separation of the coarse coal particles from the air stream. These coarse coal particles are then suitably returned to the grinding table for further pulverization, while the fine coal particles are carried through the bowl mill in the air stream, and exit therefrom along with the air.
In a conventional coal fired power generation system, a multiplicity of bowl mills of the type shown in the aforereferenced patents would commonly be employed for purposes of satisfying the requirements of the system for pulverized coal. By way of example, the capacity of each of the individual bowl mills might be on the order of 100 tons per hour of coal.
Although bowl mills constructed in accordance with the teachings of the aforereferenced patents have under actual operating conditions provided adequate performance to date, a need has nevertheless been evidenced for improvements to be made therein. More specifically, prolonged operation of this type of bowl mill has pointed up the existence of several conditions of an undesirable nature that can arise during the use thereof. One of these pertains to the means by which and the manner in which there is effectuated the bearing support of the journals on which the pulverizer rolls are mounted. To this end, the pulverizer journal systems of the type that commonly have been employed in the bowl mills heretofore have for the most part suffered from one or more of the following undesirable features. Namely, it has been found that the upper bearing has been subjected to high radial loading. On the other hand, it has been found that the lower bearing has been subjected to high thrust loading. Furthermore, it has been found that frequently the upper bearing in existing pulverizer journal bearing systems does not have the capacity required thereof for the loadings encountered thereby during service. In addition, the design of both the oil seal and the air seal has proven to be deficient. Thus, to summarize, a need has, therefore, been evidenced for a new and improved means that would be suitable for employment in a bowl mill for purposes of accomplishing the bearing support for the journals on which the pulverizer rolls are designed to be mounted.
It is, therefore, an object of the present invention to provide a new and improved journal bearing system that is suitably constructed so as to be employable in a bowl mill.
It is another object of the present invention to provide such a journal bearing system for bowl mills wherein the radial loading on the upper bearing thereof has been reduced.
It is still another object of the present invention to provide such a journal bearing system for a bowl mill wherein the thrust loading on the lower bearing thereof has been reduced.
A further object of the present invention is to provide such a journal bearing system for bowl mills wherein the capacity of the upper bearing thereof is increased.
A still further object of the present invention is to provide such a journal bearing system for bowl mills wherein the design of the oil seal has been improved.
Yet another object of the present invention is to provide such a journal bearing system for bowl mills wherein the design of the air seal has been improved.
Yet still another object of the present invention is to provide such a journal bearing system for bowl mills which is suitable for employment in newly constructed bowl mills, while yet being equally well suited for utilization in retrofit applications.